The Cancer Research
Beyond meeting the recommendation for a plant-based diet, evidence is too limited to allow any conclusions about a pesco-vegetarian diet as a specific choice for reducing cancer risk, according to AICR’s Third Expert Report.
- Overall Cancer. Evidence from long-term observational population studies shows that vegetarian diets as a whole are consistently linked to lower risk of cancer compared to diets that include meat and fish more than once a week. These vegetarian diets include pesco-vegetarian diets as well as vegan and lacto-ovo vegetarian diets and diets that include meat or fish up to once a week. Pescatarian diets specifically show a similar association with lower overall cancer risk.
- Colorectal Cancer: In a major study of U.S. vegetarians, pesco-vegetarians showed particularly low risk of colorectal cancer, even compared to people following other types of vegetarian diets. This eating pattern is likely to have higher levels of omega-3 fatty acids (the type of fat found in fish), but so far this type of fat has not been tied to lower cancer risk, so it’s not clear what might explain this association. Limited evidence suggests a potential association between fish and lower colorectal cancer (as well as liver cancer) risk, according to analysis for the AICR/WCRF Third Expert Report. Greater amounts of omega-3 fats possible with a fish-containing diet could also add benefits to reduce risk of heart disease.
Interpreting the data
After a systematic review of the global scientific literature, AICR/WCRF analyzed how plant foods and their nutrients affect the risk of developing cancer.
- Evidence categorized as “probable” means there is strong research showing a causal relationship to cancer—either decreasing or increasing the risk. The research must include quality human studies that meet specific criteria and biological explanations for the findings.
- A probable judgement is strong enough to justify recommendations.
- Evidence categorized as “limited suggestive” means results are generally consistent in overall conclusions, but it’s rarely strong enough to justify recommendations to reduce risk of cancer.
Source: AICR/WCRF. Diet, Nutrition, Physical Activity and Cancer: A Global Perspective, 2018.
Ongoing Areas of Investigation
- More on Pesco-Vegetarian Diet
What you do eat as well as what you don’t eat counts: Studies of vegetarian diets and their association with cancer risk sometimes show slightly different results. A closer look suggests that part of the difference may reflect the importance of specific food choices.
- People who follow a vegetarian diet but include frequent use of sweets, refined grains, sugar-sweetened beverages and unhealthy choices of added fats do not show as much health benefit. People following a vegetarian diet who limit these foods and include abundant vegetables, legumes (dry beans, peas, lentils, and soy foods), nuts and seeds tend to show lowest risk of cancer and heart disease.
- Overall, people in studies who follow vegetarian diets tend to also consume little or no alcohol, avoid tobacco, get regular physical activity, and maintain a healthy weight. Although researchers try to adjust for these factors in their statistical analysis, the overall lifestyle of people who follow vegetarian diets may be reflected in the health benefits seen.
- World Cancer Research Fund/American Institute for Cancer Research. Diet, Nutrition, Physical Activity and Cancer: a Global Perspective. Continuous Update Project Expert Report 2018. Available at dietandcancerreport.org.
- Orlich MJ, Chiu THT, Dhillon PK, et al. Vegetarian Epidemiology: Review and Discussion of Findings from Geographically Diverse Cohorts. Advances in Nutrition. 2019;10(Supplement_4):S284-S295.
- Segovia-Siapco G, Sabaté J. Health and sustainability outcomes of vegetarian dietary patterns: a revisit of the EPIC-Oxford and the Adventist Health Study-2 cohorts. Eur J Clin Nutr. 2019;72(1):60-70.
- Huang T, Yang B, Zheng J, Li G, Wahlqvist ML, Li D. Cardiovascular disease mortality and cancer incidence in vegetarians: a meta-analysis and systematic review. Ann Nutr Metab. 2012;60(4):233-240.
- Orlich MJ, Singh PN, Sabate J, et al. Vegetarian Dietary Patterns and the Risk of Colorectal Cancers. JAMA Intern Med. 2015.
- World Cancer Research Fund / American Institute for Cancer Research. Continuous Update Project Expert Report 2018. Diet, nutrition, physical activity and colorectal cancer. Available at: dietandcancerreport.org.
- World Cancer Research Fund/American Institute of Cancer Research. Continuous Update Project Expert Report 2018. Meat, fish and dairy products and the risk of cancer. Available at: dietandcancerreport.org.